1. Field of the Invention
This invention generally relates to a holding sealer including inorganic fibers, an exhaust gas processing device including such a holding sealer, and a manufacturing method of the same.
2. Description of the Related Art
The number of cars is greatly increasing since the beginning of this century, and the amount of exhaust gas from car engine rooms has been increasing amazingly as the number of cars has increased. Especially, various materials in the exhaust gas from diesel engines trigger environmental pollution, so that these materials are seriously influencing the global environment currently.
Under these circumstances, various exhaust gas processing devices have been suggested, and these have been used in practice. A typical exhaust gas processing device has a casing (for example, made of metal and the like) on a exhaust pipe connected to an exhaust gas manifold of the engine, in which casing an exhaust gas processing body having lots of cells, which are divided by cell walls, is arranged. Typically, these cells are constructed in a honeycomb structure. Especially in this case, the exhaust gas processing body is called a honeycomb structure body. As an example of the exhaust gas processing body, there are an exhaust gas filter such as a catalyst carrier, a diesel particulate filter (DPF), and the like. For example, in the case of the DPF, particles are trapped by cell walls during the exhaust gas passing through the exhaust gas processing body via each cell based on the above structure. Thereby particles can be removed from the exhaust gas. Materials of the exhaust gas processing body are metals, alloys, ceramics, etc. As a typical example of the exhaust gas processing body comprising ceramics, a honeycomb filter made of cordierite is known. Recently, from the viewpoint of heat resistance, mechanical strength, chemical stability, etc., a porous silundum sintered body is used as the exhaust gas processing body.
Usually, the holding sealer is placed between the above exhaust gas processing body and the casing. The holding sealer is used for protecting against breakage due to contact of the exhaust gas processing body with an inner surface of the casing during vehicle runs, and for protecting against leakage of the exhaust gas from a gap between the casing and the exhaust gas processing body. Also, the holding sealer plays an important role in preventing the exhaust gas processing body from falling off due to exhaust pressure of the exhaust gas. Moreover, the exhaust gas processing body needs to maintain high temperature for stabilizing the reaction, so that the holding sealer needs to have heat resistance. As a member satisfying these requirements, there is a sheet member including inorganic fibers such as alumina system fiber, etc.
The holding sealer is wound around at least a portion of the outer surface, except an open surface, of the exhaust gas processing body. For example, both edges of the holding sealer are engaged and the holding sealer is used by being fixed as one body with the exhaust gas processing body by means of taping. Then, the one whole body is assembled into the exhaust gas processing device by being pressed into the casing.
When the one whole body is pressed into the casing or when the exhaust gas processing device is used, surface pressure against the exhaust gas processing body exerted by the holding sealer has to be within the so-called isostatic strength in order to prevent damage to the exhaust gas processing body by compression stress from the holding sealer. Here, the isostatic strength is the compression destruction load (force) when damage occurs at the time that an isotropic resting hydraulic pressure load is applied to the exhaust gas processing body. It is defined as JASO M505-87 which is a car standard published by the Association of Corporate Car Technology.
A load that is beyond the isostatic strength is applied onto the honeycomb structure, and a method to place the holding sealer such that tab matching parts of the holding sealer are arranged facing cell walls of the honeycomb structure is suggested in order to prevent damage to the honeycomb structure at the time of combining the holding sealer wound around the honeycomb structure (see patent document 1). In the method of the patent document 1, it is disclosed that damage is unlikely to occur on the honeycomb structure because places where the surface pressure becomes high like tab matching parts of the holding sealer are arranged in a direction in which a tolerance load becomes the highest (that is, adding the surface pressure in almost perpendicular directions to cell walls) on each cell consisting of the honeycomb structure.
Patent Document 1: JP 2000-204938